RFID (radio frequency identification) radio frequency identification technology has become the focus of attention in all countries. The basic components of the system include RFID tag, RFID reader and antenna. Among them, the antenna is a device that receives or radiates the radio frequency signal power of the radio transceiver in the form of electromagnetic waves. In RFID system, antennas are divided into tag antennas and reader antennas. The goal of tag antenna is to transmit the maximum energy inside and outside the tag chip: when transmitting, the high-frequency current is converted into electromagnetic waves; When receiving, electromagnetic waves are converted into high-frequency current.
There are many manufacturing processes for RFID antennas. This paper will summarize and analyze the manufacturing technology of RFID antenna, focusing on the latest manufacturing method of RFID antenna-RFID printed antenna and related technologies, and look forward to its prospect.
Three RFID antenna manufacturing technologies
RFID antenna manufacturing technology mainly includes etching method, coil winding method and printed antenna. Among them, RFID conductive ink printing antenna is a new technology developed in recent years.
The manufacturing method of the RFID tag antenna is suitable for RFID electronic tag products with different frequencies respectively. Low-frequency RFID tag antennas are basically made by winding, and high-frequency RFID tag antennas can also be realized by the above three ways, but etching antennas are the main ones, and their materials are generally aluminum or copper.
UHF RFID tag antennas are mainly printed antennas.
Etching is also called subtractive manufacturing technology. The manufacturing process is as follows (taking the copper antenna as an example): firstly, a flat copper foil is laminated on the plastic film; Then, a photosensitive adhesive is coated on the copper foil, dried and irradiated with a positive film (pattern with required shape); Put it into a chemical developer, at this time, the bright part of the photosensitive adhesive is washed away, exposing copper; Finally, the copper is put into the etching pool, and all the copper not covered by the photosensitive adhesive is etched away to obtain the copper coil with the required shape.
Etched printed antenna has high precision, its characteristics can match the interrogation signal of reader, and it has good impedance and RF performance when applied to articles, but its only disadvantage is high cost.
When the RFID tag is manufactured by the coil winding method, the coil of the tag should be wound on the winding tool and fixed. At this time, more turns of the antenna coil are required (50- 1500 turns is typical). This method is used for RFID tags with the frequency range of 125- 134 KHz, but its disadvantages are high cost and slow production speed.
Printed antenna is printed directly on insulating substrate (film) with conductive ink to form antenna and circuit, which is also called additive manufacturing technology. The main printing methods have been extended from screen printing to offset printing, flexographic printing, gravure printing and other production methods, and the more mature production technologies are screen printing and gravure printing technology. The progress of printing technology and its further application in RFID antenna production have reduced the production cost of RFID tags, thus promoting the application of RFID electronic tags.
Compared with etched antennas and wound antennas, printed antennas have the following unique characteristics:
First, the printed antenna manufacturing can adjust the electrical performance parameters more accurately and optimize the performance of the card.
The main technical parameters of RFID tag are: resonant frequency, Q value and impedance. In order to achieve the best performance, all RFID tag manufacturing technologies can be obtained by changing the number of antenna turns, antenna size and wire diameter. Printed antenna technology can also be accurately adjusted to the required target value by locally changing the width of the line and changing the thickness of the wafer layer.
Secondly, the shape of printed antenna can be changed at will to meet the requirements of user's surface treatment.
In view of the multi-purpose use of RFID cards and the increasingly personalized requirements, printed antennas can be easily changed into any shape as needed, such as the surface of objects with different curvatures and angles, thus meeting the requirements of customers without degrading any performance.
Thirdly, printed antennas can use various card matrix materials.
Printed antenna can use different card materials according to user's requirements. Besides PVC, PET-G(*** polyester), PET (polyester), ABS (acrylonitrile butadiene styrene * * * polymer), PC (polycarbonate) and paper-based materials can also be used. If winding technology is used, it is difficult to produce RFID tags that adapt to harsh environmental conditions with materials such as PC.
4. Printed antenna manufacturing is suitable for wafer modules provided by various manufacturers.
With the widespread use of RFID tags, more and more IC chip manufacturers have joined the ranks of producing RFID chip modules. Due to the lack of uniform standards and different electrical performance parameters, the flexibility of printed antenna structure can be matched with different wafers and modules in different packaging forms to achieve the best performance.
RFID conductive ink and printed antenna technology
The reason why RFID printed antenna is superior to traditional antenna mainly depends on the characteristics of conductive ink and its perfect combination with printing technology.
Conductive ink is composed of fine conductive particles or other special materials (such as conductive polymers). ), can be printed on a flexible or hard substrate to make a printed circuit, which plays the role of a wire, an antenna and a resistor. Conductive ink largely determines the impedance of RFID printed antenna, which is an important parameter related to the performance of RFID antenna.
At present, Flint Company, Parelec Company, DuPont Company, Korean ABC Nanotechnology Company, Shanghai Yin Bao Company, Beijing Rio Tinto Technology Company and Wuhan Sanlai Technology Development Co., Ltd. have developed various conductive inks for RFID printed antennas.
According to different manufacturing processes, conductive inks can be divided into indirect conductive inks and direct conductive inks.
According to the composition of conductive factors contained in conductive ink, conductive ink includes carbon paste ink, copper paste ink, silver paste ink and gold paste ink. Silver paste ink is the best choice for RFID tags because of its low resistivity. In addition, copper is not suitable for RFID antenna printing, because its oxidation speed is very fast.
From the perspective of future development, RFID printed antenna technology will become the mainstream RFID antenna manufacturing technology, which stems from the following advantages of printing antennas with conductive ink:
low cost
The cost reduction mainly depends on conductive ink materials and screen printing process. As far as the cost of the material itself is concerned, the price of ink is lower than that of stamping or etching metal coils. Especially in the case of rising prices of copper and silver, it is an ideal alternative to print RFID antennas with conductive ink. In terms of material consumption, etching consumes a lot of metal, while conductive ink printing antenna circuit is fast, material saving, low cost and high efficiency.
One of the reasons why the screen printing process can reduce the cost is that the input of imported printing equipment is much cheaper than that of imported copper etching equipment. In addition, because the printing process does not need additional investment due to environmental protection requirements, the cost of production and equipment maintenance is also lower than that of copper etching, thus reducing the single cost of labels.
Good electrical conductivity
After the conductive ink is dried, the distance between conductive particles becomes smaller, and free electrons move to the direction of external electric field to form current, so the RFID printed antenna has good conductive performance.
Simple operation
As an additive manufacturing technology, printing technology is an easy-to-control and one-step process compared with subtractive manufacturing technology (such as etching).
contamination free
Chemical reagents, such as photosensitive glue, which must be used in the copper etching process, have a strong corrosive effect, and the generated wastes and emissions have caused great pollution to the environment. Conductive ink is used to print directly on the substrate without using chemical reagents, so it has the advantage of no pollution.
The choice of substrate is flexible and diverse.
Conductive ink can be printed on almost all printing materials, including polyester, polyimide, ABS engineering plastics, PVC (polyvinyl chloride), polyethylene, polypropylene, polycarbonate, cardboard and so on. However, copper etching technology can only use substrates with high corrosion resistance, such as polyester, which is generally more expensive than the substrates selected for printing.
The printed conductive ink antenna can also withstand higher external mechanical pressure. In addition, the RFID tag printed antenna made of conductive ink has better elasticity and higher reliability.
When using conductive ink to print RFID antenna, you need to pay special attention to the following operations to achieve the best printing effect.
Operating environment: the choice of printing environment directly affects the printing effect. Dust and foreign body pollution in the printing area should be minimized, and the environmental requirements should be at least 100000 clean room.
Pretreatment: Ensure that the printed surface is clean, pollution-free, free of grease and oxide. The shorter the residence time after treatment, the better to prevent oxidation or pollution.
Dilution: After adjusting the viscosity of ink, adding a small amount of diluent can improve the printing effect of automatic printing. Stir thoroughly before use 10 minute.
Pre-drying: the temperature and time can be adjusted according to the specific production process.
Storage: Store at 20-25 degrees, away from light and heat.
It can be seen that the process requirements of making RFID printed antenna with conductive ink are higher. For conductive ink itself, it should have the characteristics of strong adhesion, low resistivity, low curing temperature and stable conductivity to meet the functional requirements of RFID antenna.
Application value of RFID printed antenna
At present, RFID technology has been applied to logistics, retail, military, urban management, book management, food safety traceability and other fields. Especially in the retail field, RFID tags are added to the packaging of goods by many retailers because of their advanced technology and convenient management, so as to track the flow of goods in real time. Wal-Mart, Metro and other major international retailers require their suppliers to put RFID tags on their products.
Therefore, RFID and related technologies need to be constantly improved to meet the application needs of different industries and fields. Using conductive ink and advanced RFID antenna printing technology can optimize the application value of RFID electronic tags and further promote the application of RFID. Therefore, the application value of RFID antenna printing technology mainly focuses on the following two aspects:
First, reduce the tag cost and promote the application of RFID in various industries.
The high tag cost has always been a difficult problem for RFID industry and users, and RFID tag cost accounts for the largest proportion in all aspects of RFID. Therefore, in the process of popularization and application of RFID electronic tags, how to reduce the tag cost and improve the tag performance is a top priority.
For general commodities, the use of RFID tags will lead to the increase of product cost, thus hindering the further application of RFID technology. And conductive ink technology can make RFID applications out of the cost bottleneck. Using conductive ink to print RFID tag antenna can greatly reduce the manufacturing cost of HF and UHF antennas, thus reducing the overall cost of RFID tag.
Conductive ink RFID printed antenna has been applied to RFID electronic tag tickets used in public transportation system in China. Product anti-counterfeiting in medicine and other fields is also an area where RFID electronic tags can show their talents. The reduction of label price makes it possible to be widely used in the anti-counterfeiting system of high value-added products such as medicine and alcohol.
Secondly, promote the development of printing industry.
Besides conductive ink, the production of RFID antenna also needs the help of advanced printing technology. This undoubtedly broadens the development direction and road for printing industry, which is no longer limited to traditional paper printing, but intersects with automatic identification industry and semiconductor industry, which can promote the progress of all industries.
In addition, in order to cooperate with the development of RFID tag technology and conductive ink RFID printing antenna, the printing industry will continue to develop more advanced printing technology, thus promoting the rapid development of the printing industry itself.
With the development of conductive ink and printing technology, RFID printed antenna technology will be popularized and widely used, and the cost of RFID tags will be further reduced, thus promoting the application of RFID technology in more fields.